VFD Startup after long shutdown

     To ensure the better performance of VFD, Startup is very essential to avoid the unexpected damage or failures after a long/short shutdowns. Following startup maintenance of VFD and field devices must be carried out during the startups.

Checking and Cleaning

  • Check if drive or panel is free from Dust,Oil, Mist and Harmful gases,Liquid
  • Clean & remove the clogs if any in the VFD panel air suction louvers 
  • Use a suction type Vacuum pump to remove any dust content settled down or to remove spider cobwebs if any present around the panel or VFD 
  • Check the Conditions of  all cable free from Damage/Cut
  • Check the drive cooling fan working condition
  • Check and Clean the VFD Heat-sink for better heat dissipation 
  • Ensure that no cable cut pieces or wire strands are lying near or inside VFD panel

Inspection of the VFD and Field conditions  

VFD to Field device
  • Verify the tightness of Power cable and Earth Cable
  • Check the continuity of input and output cables for any damage caused due to unwanted circumstances 
  • Check VFD I/O terminals and relay output cables tightness 
  • Check the cable tightness of Field Inputs and outputs
  • Components requiring lubrication must be re-inspected for dried up lubrication to prevent mechanical failures while powering on 
  • Check the tightness of cables and presence of rust on the components. Verify resistance of the DBR before powering on  (If DBR presence)
  • Check all brake/mechanical interlocks controlled by the VFD are properly wired and are functioning properly 
  • Visually check the condition of Motor winding and Cables for any sign of damage or corrosion

  Earthing Test 

Earth testing using ohm meter
  • Ensure to measure earthing resistance in the main earth pit against next pit after removing VFD earthing by using milli Ohm meter. Confirm ground resistance value of 5 Ohms or less as per IEEE standard 
  • Ensure to check the continuity of main Earth pit, motor earthing, panel earthing and VFD earthing. All should be in equipotential line

 IR Test

Insulation resistance b.w terminals
  • Disconnect VFD output cables and keep motor is connected 
  • Carry out the Megger test against U, V, W cable terminals with respect to Earthing and note the reading. (Test voltage 500/1000V)
  • Insulation resistance should be >1MΩ for a duration of 3 seconds
           Do not use Megger to VFD as it may damage the VFD internal components

 VFD Cold Test

         With the help of a True RMS multi-meter which has Diode mode available, perform a cold check on the Diode and IGBT on the VFD before powering on.

          Click here to know how to carry out VFD cold test 

 After Powering up the VFD 

Powered VFD to field
  • Power-up the VFD without any Run command for 15 minutes and allow the capacitor to charge uniformly.
  • Check the DC bus voltage. It should be 560 ~ 570 VDC
  • Check any abnormal noise,vibration or abnormal in operations
  • Before giving the Run command ensure all interlocks are working as per requirement 
  • After all checkpoints are verified, run the equipment on no load condition and observe the operation for 30 Mins for any abnormality
  • Check motor direction when forward/reverse command is fed 
  • Check and perform No load operation and check VFD No load current. 
  • Run the motor at slow speed and check the performance then gradually increase speed and check the operations
  • Check for excessive vibration and shock loading 
  • Measure & confirm the currents are balanced in each phase (U, V, W) after full load or desire load of process requirement 
  • if everything is found ok, Resume normal operation 

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